The invention relates to anionic cellulose ethers and to the use of said ethers as associative thickeners, rheology modifiers or stabilizers.
Associative thickeners, rheology modifiers, and stabilizers for emulsions and suspensions are used in many applications including water-based paints, (oil) drilling, paper making, (laundry) detergents, and personal care products or cosmetics. However, most compounds typically used in these applications suffer from the disadvantage that the viscosity of the composition decreases with increasing temperature. In other words, the performance of these compounds is poorer at higher temperatures, typically in the range of 20 to 60xc2x0 C.
EP-A1-0 853 159 relates to a process and a coating colour for coating a cellulosic web. It is described that the coating colour contains an aqueous polymer whose viscosity in an aqueous solution increases when the temperature rises. Preferably, methyl cellulose is used. In FIG. 3 it is shown that carboxymethyl cellulose is not subject to an increase in viscosity with increasing temperature.
Although this document does not pertain to anionic cellulose ethers of the type disclosed below, it describes the effect which is also desired in the present application. A drawback to the use of the cellulose ethers disclosed in EP-A1-0 853 159 is that with increasing temperature the solubility of the polymer is lost completely. In fact, the transient increase in viscosity is caused by the loss of solubility of the polymer with increasing temperature. Hence, it is the aim of the present application to provide alternatives to these polymers which do not have this disadvantageous property.
Anionic cellulose ethers are known in the art. There are several documents showing that hydrophobically modified cellulose ethers have associative properties and cause thickening of compositions containing them.
EP-A1-0 566 911 pertains to hydrophobically modified polysaccharide ethers, having a molecular weight of 10,000 to 300,000, which are substituted with hydrophobic alkyl or alkaryl groups having 8 to 24 carbon atoms and which can be used as associative thickeners in aqueous protective coatings. Table 4 discloses carboxymethyl hydroxypropyl starch substituted with C18 hydrophobic groups and carboxymethyl hydroxyethyl cellulose substituted with C16 hydrophobic groups. These compounds were prepared, according to the footnote of Table 4, by reacting carboxymethyl hydroxypropyl starch and carboxymethyl hydroxyethyl cellulose with stearyl isocyanate using dimethyl sulfoxide as a solvent.
JP-A-09110901 relates to carboxymethyl polysaccharide ethers substituted with a C8-C40, optionally branched alkyl or alkenyl glycidyl ether and their use as a thickening agent for cosmetics and toiletries. In Examples 1-14, carboxymethyl hydroxyethyl cellulose, carboxymethyl methyl cellulose, and carboxymethyl hydroxypropyl starch substituted with stearyl, palmityl, behenyl or isostearyl glycidyl ether groups are disclosed. These compounds are prepared by reacting the polysaccharide, e.g. hydroxyethyl cellulose, with the glycidyl ether, followed by carboxymethylation.
Similar types of compounds, e.g. carboxymethyl hydroxypropyl methyl cellulose substituted with stearyl glycidyl ether groups, and preparative processes are described in JP-A-05331201. Said compounds are reported to be used as thickening agents in cataplasm and cosmetic compositions.
WO 97/31950 pertains to carboxymethyl cellulose ethers substituted with long-chain groups and their use as thickening additives for aqueous compositions such as paints, plasters, and cosmetics. On page 7 of this document said cellulose ethers are reported to possess high associative properties. In Example 1, carboxymethyl cellulose is reacted with 1-epoxyoctadecane and in Example 19; carboxymethyl cellulose is reacted with dodecyl glycidyl ether.
DE-A1-3927567 pertains to the use of hydrophobically modified cellulose ethers for stabilizing aqueous coal slurries. These cellulose ethers are substituted with hydrophobic groups having at least six carbon atoms in the form of, inter alia, 3-alkoxy-2-hydroxypropyl and 2-alkyl-2-hydroxyalkyl groups. In column 4, lines 15-16, n-butyl glycidyl hydroxyethyl cellulose is exemplified.
EP-A2-0 295 628 relates to water-soluble 3-alkoxy-2-hydroxypropyl derivatives of hydroxyethyl, hydroxypropyl, and methyl cellulose ethers and their use in building compositions. The alkyl group is a straight- or branched-chain alkyl group having 2 to 8 carbon atoms. As is shown in Example 1, these compounds are prepared in a slurry process by reaction of hydroxyethyl cellulose with n-butyl glycidyl ether.
However, none of these prior art documents describes the desired viscosity-temperature relationship explained above. It is further expected that the cellulose ethers which are disclosed in these documents will have decreasing viscosity with increasing temperature.
EP-A1-0 541 939 discloses a number of 3-allyloxy-2-hydroxypropyl ethers of celluloses substituted with other ether groups including methyl 3-allyloxy-2-hydroxypropyl cellulose, hydroxyethyl 3-allyloxy-2-hydroxypropyl cellulose, and carboxymethyl 3-allyloxy-2-hydroxy-propyl cellulose. These water-soluble cellulose ethers are polymerizable, which may be advantageous in some applications. However, cellulose ethers containing allyl groups are unstable compounds and will decompose gradually upon storage. This, obviously, is a disadvantage and for this reason such compounds are not desired for use in applications in accordance with the present invention.
Surprisingly, we have found anionic cellulose ethers which show a lesser decrease, or even an increase, in viscosity with an increase in temperature, and this effect is believed to be due to a reversible temperature-dependent association. Furthermore, unlike some of the (associative) thickeners of the prior art, the compounds of the invention retain their good water solubility even at higher temperatures. These properties make them particularly suitable for use in the applications mentioned above, in particular in drilling operations in which they are expected to reduce fluid loss.
The anionic cellulose ether according to the present invention is obtainable by a process comprising reacting an alkali metal cellulose with
one or more reagents A selected from the group consisting of haloacetic acids, alkali metal haloacetates, alkali metal vinyl sulfonates, vinyl sulfonic acid, and precursors thereof, and
one or more reagents B having the formula R1xe2x80x94(OCH2CH(R2))n-P,
wherein
R2 represents hydrogen or a methyl group,
n is 0-2,
P represents a glycidyl ether group, a 1,2-epoxy group or a precursor thereof, if P represents a glycidyl ether group, R1 represents a linear C3-C5 alkyl group, optionally containing an oxygen atom, a phenyl group or a benzyl group, if P represents a 1,2-epoxy group, R1 represents a linear C3-C5 alkyl, optionally containing an oxygen atom,
with the proviso that in the process no use is made of a reagent having the formula R3xe2x80x94(OCH2CH(R4))m-Q, wherein R3 represents a C8-C30 group, R4 represents hydrogen or a methyl group, m is 0-10, and Q represents a glycidyl ether group, a 3-halo-2-hydroxypropyl ether group, a 1,2-epoxy group or a halide.